CONTENTS 3X 



XV. Water Requirements for Plant Growth 183 



Water Requirements of Plants — Precipitation and Plant 

 Growth — Ecological Classification and Crop Production, 

 Xerophytes, Mesophytes, Hydrophytes — Plant Succes- 

 sions — Plant Geography — Crop Zones. 



XVI. Relation op Carbon Dioxide to Plant Growth 192 



Source of Carbon — Composition of the Air — Absorption of 

 Carbon Dioxide — The Colls the Laboratories of the Plant 

 — Composition of Chlorophyll — Relation of the Stomata 

 to Carbon Dioxide — Photosynthesis — Efficiency of the 

 Food-making Machine — Sugar and Starch Transformation 

 and Migration — Formation of Other Foods. 



XVII. Mineral Nutrients and Nitrogen 199 



Ash Content of Plants — Origin of Minerals — The Functions 

 of the Mineral Nutrients — Chemical, Analysis of Plants and 

 Soils — Nitrogen — Source of Nitrogen — Ammonifi.cation — 

 Nitrification — Nitrifying Organisms — Other Soil Organ- 

 isms — ^Water Cultures. 



XVIII. Metabolism — Digestion — Translocation — Growth 209 



Metabolism — Digestion — Translocation — Assimilation — 

 Growth — Phases of Growth — Irritability — Plant Move- 

 ments — Tropisms — Relation of Plant Organs to Sunlight. 



XIX. Respiration — Aeration — Fermentation 221 



Respiration — Respiration and Photosynthesis — Respira- 

 tion and Starvation — Diffusion and Absorption of Oxygen 

 — Aeration — Fermentation — Anaerobic Respiration. 



XX. Temperature and Light 228 



Environmental Factors — Plant Geography — ^Temperature 

 — Maximum, . Optimum and Minimum Temperature for 

 Germination — Freezing — Light — Relation of the Plant to 

 Sunlight — Relationship of Leaves to Sunlight — Influence 

 of Light on Plant Distribution. 



XXI. Plant Evolution 235 



Geological Record — Geographical Record — Theories of 

 Evolution — Lamarck — Darwin — Mendel — DeVries. 



